1. Field of the Invention
The present invention relates to a capacitive chemical sensor that uses an ion exchange surface to detect analyte ions in a liquid medium.
2. Description of the Prior Art
Various capacitive sensors are taught in the art to detect humidity in the air or anesthetic gas in a gas mixture delivered to a patient during various medical procedures U.S. Pat. No. 3,350,941 issued to K. W. Misevicc et al. and U.S. Pat. Nos. 4,203,087 and 4,277,742 issued to Kovac et al, disclose capacitive humidity sensors. These humidity sensors use a moisture sensitive layer which absorbs water vapor. The dielectric property of the layer changes as it is penetrated by water vapors. As the moisture content of the air increases the capacitance of the humidity sensor increases.
U.S. Pat. No. 4,453,126 issued to G. A. Volgyesi and a published U.K. patent application GB No. 2 137 361 A, teach an apparatus for measuring anesthetic gas in a breathing mixture supplied to a patient. For both references, a planar capacitor is coated with a polymeric or lipid layer. The physical or chemical properties of the polymeric or lipid layer change with increasing concentration of the anesthetic gas, causing a change in the dielectric constant of the layer.
Similarly, U.S. Pat. No. 4,264,331 issued to Klein et al discloses an air pollutant and/or fire combustion sensing apparatus using a capacitive sensor. Physical absorption of the analyte gas into a coating changes the dielectric properties of the coating.
A related U.S. patent application filed by Arnold L. Newman on Nov. 19, 1985, entitled "Capacitive Chemical Sensor for Chemical Analysis and Measurement" (Ser No. 799,716) discloses a capacitive chemical sensor utilizing biochemical bonding systems; another related application filed by the present inventors and entitled "Capacitive Chemical Sensor for Detecting Certain Analytes, including Hydrocarbons in a Liquid Medium" discloses a capacitive chemical sensor relying on the affinity of an "active layer" for analyte molecules in solution.